Abstract

In this chapter, our recent research about the impact of hydrogen passivations and size on the electronic and optical features of silicon quantum dots will be reviewed. A theoretical modeling will be presented for silicon quantum dot with spherical topologies and treating their corresponding physical properties. This recent study was conducted by means of first principle calculations to explore the energy band gap versus the radius of Si quantum dots for passivated and non-passivated surface. The optimization of the structures of quantum dots was performed for both passivated and unpassivated quantum dots with various sizes. The interesting features for the electronic characteristic, such as the energy band gaps are higher in the case of hydrogenated surface than the unpassivated case. Accordingly, both quantum confinement and surface passivation provide information concerning the electronic and optical characters of Si quantum dots. The passivation impact on the surface dangling bonds with hydrogen atoms as well as the contribution of surface states on the gap energy are also presented. The hydrogen passivation influence increases the energy gap than that of pure silicon quantum dots. The significant character of the confinement and surface passivation on the optical properties are reviewed. The previous experimental determinations have shown that the optical properties of these dots were significantly affected by the quantum confinement effects. Overall, the hydrogen saturation surface controls principally the ground-state geometry, the energy gap, and optical absorption of Si quantum dots with the change of radius size. It was inferred in our previous study that the insertion of hydrogen could lead to the alteration of the electronic structure of silicon quantum dots. The saturated surface by hydrogen atoms has also a main contribution on the spatial distribution of the highest occupied and lowest unoccupied molecular orbitals. The hydrogen effect on optical absorption spectra and the static dielectric constant are also reviewed. Exclusively, the absorption threshold relationship of Si nanoparticles on the radius and hydrogenation surmise a decrease in the quantum confinement effect. The absorption spectra illustrated that the absorption properties are intimately accompanied with the surface saturation as well the radius of the dots. This theoretical finding could assist the comprehension of the microscopic mechanism which is spectacular for the devices performance and the potential application in nanotechnologies. This could highlight the significant optical parameters of silicon quantum dots for the purpose to comprehend the optical properties in the photoluminescence process of finite-size dots. The recent work about the optical absorption showed that the nanostructured Si could possess a very high luminescence in the visible regime as reported in the experimental inspection.